[mkgmap-dev] HGT - getElevation()

Wed Jan 10 16:53:46 GMT 2018

I don't think rounding or interpolating
will deliver any better results.
If you have 1" .hgt files, you get
an altitude value every 30m.
With 3" .hgt files much worse, every 90m.
In the mountains, between 2 points
may be a big wall with some 100m
height-difference.
So if you have small deviations in lat/lon,
you will evtl. get very false elevation values.

If you interpolate altitude-values,
you calculate wrong values by design :-(

May be I'm wrong, but this is my theory.

lg Peter

Am 10.01.2018 um 17:39 schrieb Gerd Petermann:
> Hi Andrzej,
> 
> if you want to try this:
> you can easily change the code in interpolatedHeight to return the height in feet, just make sure that you don't convert UNDEF.
> 
> The only other change that is needed is  in this line in DemHeader:
> writer.putInt(0); // 0: elevation in metres, 1: foot
> 
> well, the comment should say feet , not foot
> 
> Gerd
> 
> ________________________________________
> Von: mkgmap-dev <mkgmap-dev-bounces at lists.mkgmap.org.uk> im Auftrag von Frank Stinner <Frank.Stinner at kabelmail.de>
> Gesendet: Mittwoch, 10. Januar 2018 17:27:22
> An: mkgmap-dev at lists.mkgmap.org.uk
> Betreff: Re: [mkgmap-dev] HGT - getElevation()
> 
> Hi Gerd and Andrzej,
> 
> i think "overkill" is a good word.
> 
> For algorithm that'a only numbers, it does not matter. The questions is, how exact are the hgt-values. We don't know that, but i don't believe it is
> +-1m or so. I'm not wondering, when the hgt's have +-5m or +-10m. The copernicus-data have +-7m and i don't believe the technic was worse.
> 
> That's why feets are overkill. The numbers are 3 times greater, that's why the dem's are greater. It's not worth it.
> 
> 
> Frank
> 
> ---
> Diese E-Mail wurde von Avast Antivirus-Software auf Viren geprüft.
> https://www.avast.com/antivirus
> 
> 
> _______________________________________________
> mkgmap-dev mailing list
> mkgmap-dev at lists.mkgmap.org.uk
> http://www.mkgmap.org.uk/mailman/listinfo/mkgmap-dev
> _______________________________________________
> mkgmap-dev mailing list
> mkgmap-dev at lists.mkgmap.org.uk
> http://www.mkgmap.org.uk/mailman/listinfo/mkgmap-dev
> 